Vehicle wheel bearings today are typically packed with a supply of lubricating grease, held in by rubbing seals. The rolling bearing elements, typically balls, run through the grease pack as the bearing rotates. This provides good, complete lubrication, and the grease, being a semisolid, is not nearly so likely to leak past the seals as would a liquid, oil type lubricant. This allows so called "sealed for life" designs. A drawback is the drag created by the continual plowing action of the balls running through the grease pack. This drag is translated into extra heat. Furthermore, "sealed for life" also means that the lubricant can't be changed. Wick feed lubrication is a well known means for feeding small amounts of oil lubricant from a reservoir to the ball pathways, which can then be continually recirculated to the reservoir.
Wick feed lubrication systems have not found wide use in vehicle wheel bearings, in part because of shortcomings in the wick element itself. The wick is a soft, oil absorbent material capable of capillary action. As a consequence, it is soft, with little internal rigidity. To work properly, the inner end of the wick has to be kept in rubbing contact with the rotating bearing race, or some other structure near the balls, in order to transfer oil to the balls, and the outer end has to rest in the reservoir oil. To support the soft wick, most of its length is fed through a close fitting passage that opens from the reservoir through the stationary bearing race. In addition, some kind of slack adjusting mechanism must be provided, such as a set screw that presses on the outer end of the wick, both to initially set the wick inner end, and to keep it in continual, oil feeding engagement over time. Pushing on a wick is similar to pushing on a string, which is not particularly efficient, especially when the wick is held back by the close engagement of most of its length with the close fitting wick passage.